1. Field of the Invention
The invention relates to power supplies, and in particular relates to voltage regulators regulating direct current (DC) output voltages using analog-to-digital converters.
2. Description of the Related Art
Switched mode power supplies or adapters are widely used to power electronic devices as well as charge batteries for mobile devices such as wireless phones, palm top computers, toys, etc. The output voltage of the power supply must be regulated within a specified range depending on the devices being powered. Typically this requires that the switched mode power supply includes components at the output of the power supply that sense the output voltage and provide feedback for a switched mode power supply controller or regulator which adjusts the power supply operation accordingly to maintain output regulation.
FIG. 1 is a schematic block diagram of a conventional DC to DC converter having multiple DC outputs, as disclosed in U.S. Pat. No. 6,204,651 to Marcus et al. The DC to DC converter includes a differential comparator 10, a combining module 12, a comparator 14, a decimator 16, an interpolator 18, an expanded switching module 20, an external element 21, a source 22, a first load 24, a second load 26, and a differencing module 28.
Load 24 produces a first output voltage and load 26 produces a second output voltage. The combining module 12 receives the first and second output voltages, or representations thereof, and produces a combined output voltage by combining first and second output voltages in a fixed ratio. The representative combined voltage is received by comparator 14. Comparator 14 produces the digital stream of comparison data according to the representative combined voltage and a reference voltage Vref.
The decimator 16 receives the digital stream of comparison data and produces a digital stream of charged data and load data to interpolator 18. Here, combining module 12, comparator 14, and decimator 16 comprise a first electrical path for interpolator 18 to determine charge or load operation.
The differencing module 28 receives the first and second voltages to produce a representation of the first and second voltages. The differential comparator 10 compares the representation of the first and second output voltages, and provides a feedback signal to interpolator 18 through a second electrical path indicating whether the first output voltage or the second output voltage is to be load destination for the external element 21. For example, if the first output voltage is lower than the second output voltage, then the load signal 182 corresponding to load 24 will be active during the given set of clock cycles, and if the first output voltage exceeds the second output voltage, then the load signal 181 corresponding to load 26 will be active during the given set of clock cycles.
The interpolator 18 receives the digital stream of charged data, load data through the first electrical path, and the output of the differential comparator 10 through the second electrical path, and produces load signals 181 and 182 and charge signal 183.
When the charge signal 183 is enabled, the N-channel transistor 201 in switching module 20 is enabled while the P-channel transistors 203 and 205 are disabled. In this configuration, the external device 21 is charged by the source 22. When the load signal 181 is enabled and the charge signal 183 is disabled, the P-channel transistor 203 of switching module 20 is turned on, while the N-channel transistor 201 is turned off. In this configuration, the external element 21 is coupled to the load 26 and the source 22 such that it discharges energy into the load 26, increasing the second output voltage. When the load signal 182 is enabled and the charge signal 183 is disabled, the P-channel transistor 205 of switching module 20 is turned on, and the N-channel transistor 201 is turned off. In this configuration, the external element 21 is coupled to the load 24 and the source 22 such that it discharges energy into the load 24, increasing the first output voltage.
The interpolator 18, based on the feedback comparator 10 and the digital stream of charge data and load data, enables the charge signal 183 and load signal 181 or load signal 182. Accordingly, when the differential comparator 10 provides feedback to interpolator 18 that the first output voltage is to be regulated, the interpolator 18 enables the load signal 182. Similarly, when the differential comparator 10 provides feedback to interpolator 18 that the second output voltage is to be regulated, the interpolator 18 enables load signal 181. Thus, for any given set of clock cycles, interpolator 18 will enable the charge signal 183 and either load signal 181 or load signal 182.
However, an additional differential comparator 10 and combining module 12 are required to determine which load should be regulated, consuming power and increasing cost. In addition, interpolator 18 enables the charge signal 183 and load signal 181 or load signal 182 according to the data received from the first and second electrical paths, which may destabilize the generated voltage unstable.